Enhancing light absorption of graphene with dual quasi bound states in the continuum resonances

Graphene is promising for next-generation optoelectronic devices owing to its unique optical and electronic properties whereas relatively weak light-matter interaction limits its performance. In this work, light can be absorbed totally by graphene with the aid of single layer all dielectric metasurface in the near infrared region. The metasurface is composed of periodically arranged amorphous Silicon nanocuboids quadrumer suspended in air which supports resonances governed by symmetry protected bound states in the continuum. Symmetry perturbation is introduced to the metasurface to induce quasi bound states in the continuum resonances by elements pair movement method in x or/and y direction. Light absorption performance of the hybrid structure can be enhanced to 50% at single-mode critical coupling state and 100% at dual-mode degenerate critical coupling state. Temporal coupled mode theory is used to analyze physical mechanism of max absorption Amax for both single mode and dual mode condition in two-port system as an analog of transparent hybrid structure. Furthermore, absorption performance can be tuned by varying the elevation between graphene and metasurface. Effects of metasurface's geometric parameters including scaling factor and thickness on absorption characteristics are also explored. Our results may provide a new route for enhancing light absorption of graphene or other 2D materials which may facilitate to design advanced modulators and photodetectors.